diff --git a/src/common/compat_strlcpy.h b/src/common/compat_strlcpy.h
index a293142a..d97e405c 100644
--- a/src/common/compat_strlcpy.h
+++ b/src/common/compat_strlcpy.h
@@ -32,5 +32,6 @@ THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #ifndef HAVE_STRLCPY
+#include <stddef.h>
 size_t strlcpy(char *dst, const char *src, size_t siz);
 #endif